The common defining factor of coronae is a distinct annulus of tectonic origin. Current coronae classification is based on an intensive study of coronae primarily with maximum widths in excess of 100 km. Topographically coronae with maximum widths in excess of 250 km tend to exhibit raised interiors with exterior rim and moat structures, which may or may not correspond to coronae annuli. These coronae are believed to be the result of gravitational relaxation of a diapir or hot-spot generated uplift. This mode of formation however, does not account for small coronae, coronae with diameters less than 200 km, that tend to exhibit depressed interiors with down-dropped or topographically level annuli. These small coronae represent caldera-like activity on Venus.